During a vehicle collision, torque-transmitting shafts within the vehicle, such as the drive shaft or steering shaft, can pose a danger to occupants if an axial collision force applied to the shaft breaks the shaft free from its mountings and drives the shaft into the passenger compartment. To reduce the potential danger posed by such components, shafts have been constructed so as to be collapsible in an axial direction by plastic deformation of the shaft upon application of an axial force of sufficient magnitude. In general, the shaft is formed with one or more regions of reduced axial strength, so that the shaft will collapse in a controlled and predictable manner at such regions.
Hydroforming of vehicle components is conventionally known to those skilled in the art. In the hydroforming process, a blank, typically a piece of elongated, tubular metal stock, is placed in a hydroforming die having die surfaces with shapes and features corresponding to those desired of the finished component. Both ends of the blank are sealed, and hydroforming fluid is injected into the blank under pressure, thereby expanding the blank into conformity with the die surfaces. Hydroforming methods are described in U.S. Pat. Nos. 5,107,693, 5,233,854, 5,333,775, 4,567,743, 5,070,717, 5,239,852 and 5,339,667, the disclosures of which are hereby incorporated by reference as preferred methods by which hydroforming in accordance with the present invention may be accomplished.
Hydroforming is an advantageous method for forming metal vehicle components, because the process is efficient and economical and produces repeatable accuracy in the components formed. The prior art has not, however, suggested a process for hydroforming a collapsible shaft having torque transmitting splines, wherein the splined portion of the shaft has an outer diameter that is smaller than an inner diameter of an adjacent portion of the shaft, so that the splined portion can deform into the adjacent portion when the shaft is subjected to an axial force of sufficient magnitude.
It is an object of the present invention to provide a hydroformed collapsible shaft and a method for hydroforming a collapsible shaft. The invention, in one form, includes a method of forming a collapsible driveshaft comprising the steps of placing a tubular metal blank into a hydroforming die having a die cavity and expanding the tubular metal blank by sealing opposite ends of said blank and pressurizing an interior of the blank with hydroforming fluid. A first portion of the blank is expanded to a first outer diameter and is engaged with surfaces of the die cavity defining splines so that splines are formed on the first portion. A second portion of the blank is expanded to a second outer diameter and an inner diameter which are both greater than the first outer diameter of the first portion.
The invention, in another form, includes a method of forming a collapsible driveshaft. A first tubular metal blank is placed into a first hydroforming die having a first die cavity. The first tubular metal blank is expanded into conformity with surfaces of the first die cavity by sealing opposite ends of the first tubular metal blank and pressurizing an interior of the first tubular metal blank with hydroforming fluid to form a first hydroformed member having splines on an exterior surface of one end portion thereof and a first connecting portion on an opposite end portion thereof.
A second tubular metal blank is placed into a second hydroforming die having a second die cavity. The second tubular metal blank is expanded into conformity with surfaces of the second die cavity by sealing opposite ends of the second tubular metal blank and pressurizing an interior of the second tubular metal blank with hydroforming fluid to form a second hydroformed member having connecting portion on one end portion thereof. The second connecting portion is cooperatively engageable with the first connecting portion of the first hydroformed member.
The first connecting portion of the first hydroformed member is engaged with the second connecting portion of the second hydroformed member so as to couple the first and second hydroformed members together so that rotation of one of the hydroformed members about a longitudinal axis thereof translates into rotation of the other of the hydroformed members.